Dressing jig for glass substrate polishing pad

ABSTRACT

Dressing treatment of a polishing pad, adjusting a polishing surface of the polishing pad to given flatness and surface roughness without deteriorating productivity, a method for polishing a glass substrate, including polishing a main surface of a glass substrate using the polishing pad adjusted by the dressing treatment, and a method for manufacturing a glass substrate using the polishing method are provided. A dressing jig having arithmetic surface roughness on a surface performing dressing treatment of from 0.10 μm to 2.5 μm is used as the dressing jig for adjusting a polishing surface of the polishing pad to given flatness and surface roughness. A main surface of the glass substrate is polished with the polishing surface of the polishing pad having been subjected to a dressing treatment using the dressing jig.

FIELD OF THE INVENTION

The present invention relates to a dressing jig for a polishing pad for polishing a glass substrate, a method for polishing a glass substrate using the dressing jig, and a method for manufacturing a glass substrate.

BACKGROUND OF THE INVENTION

To finish a main surface of a glass substrate in a smooth mirror surface, polishing of the glass substrate using a polishing pad is performed. One example of the polishing includes a method for polishing a main surface of a glass substrate, comprising placing a polishing pad comprising a polyurethane resin or the like on a platen surface of a polishing apparatus, subjecting a polishing surface of the polishing pad to dressing treatment using a dressing jig to obtain given flatness and surface roughness, and relatively moving the glass substrate and the polishing pad in a state that the polishing surface of the polishing pad is pressed against the main surface of the glass substrate while supplying a polishing slurry containing abrasives between the glass substrate and the polishing pad.

Patent Documents 1 to 3 propose a method of using a diamond dressing jig comprising a base substrate such as stainless steel and diamond abrasives of nearly #400 fixed to the surface of the base substrate, as a dressing treatment of a polishing pad. However, in the proposed method, the surface of the polishing pad just after the dressing treatment is rough, and the dressing treatment must again be conducted separately using a smooth substrate having arithmetic average roughness Ra of less than 0.1 μm until the polishing surface of the polishing pad has a given surface roughness. Thus, the proposed method has poor productivity.

-   Patent Document 1: JP-A-2008-112572 -   Patent Document 2: Japanese Patent No. 4234991 -   Patent Document 3: JP-A-2003-117823

SUMMARY OF THE INVENTION

The present invention has objects to provide a dressing jig suitable for polishing a glass substrate, a method for polishing a glass substrate using the dressing jig, the method having excellent productivity, and a method for manufacturing a glass substrate.

The present invention provides a dressing jig for a glass substrate polishing pad, having a plate shape and dressing a polishing pad for a glass substrate with a plate surface thereof, wherein the plate surface has a surface roughness of from 0.10 μm to 2.5 μm in terms of arithmetic average roughness Ra. The present invention further provides a method for polishing a glass substrate, the method comprising dressing a polishing pad for a glass substrate using the dressing jig for a glass substrate polishing pad, and polishing a glass substrate with the polishing pad for a glass substrate. The present invention further provides a method for manufacturing a glass substrate, comprising the method for polishing a glass substrate, as an essential step.

The dressing jig according to the present invention has a specific surface roughness. As a result, the dressing jig does not require a separate dressing jig (for example, a smooth substrate having arithmetic average roughness Ra of less than 0.1 μm), and can adjust a polishing pad for a glass substrate to a desired state. Therefore, use of the dressing jig of the present invention (hereinafter referred to as the “present dressing jig”) can provide a polishing method having excellent productivity.

The glass substrate manufactured by polishing a glass substrate using a polishing pad having been subjected to a dress treatment with the present dressing jig having a specific surface roughness has excellent micro waviness characteristics and arithmetic average roughness characteristics of a main surface thereof. Furthermore, the polishing pad having been subjected to a dressing treatment using the present dressing jig has subsidiary effects that water-soluble polymers and surfactants remaining in the polishing pad can efficiently be removed and decrease in polishing efficiency due to the residual materials can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 are views showing one example of the present dressing jig. FIG. 1A is a schematically perspective view of the present dressing jig, and FIG. 1B is a cross-sectional view of the present dressing jig.

FIG. 2 are schematically cross-sectional views of a polishing pad after a dressing treatment. FIG. 2A is a schematically cross-sectional view of the polishing pad in which a polishing surface of the polishing pad is not adjusted to given flatness and surface roughness, and FIG. 2B is a schematically cross-sectional view of the polishing pad in which a polishing surface of the polishing pad was adjusted to given flatness and surface roughness.

FIG. 3 is a view showing measurement sites and measurement regions of micro waviness μWa.

FIG. 4 is a view showing measurement sites and measurement regions of micro waviness Wq.

FIG. 5 is a view showing measurement sites and measurement regions of average surface roughness Ra.

FIG. 6 is a graph showing change with the passage of time of the degree of coagulation of a polishing slurry after a dressing treatment.

DETAILED DESCRIPTION OF THE INVENTION

Polishing of a glass substrate using a polishing pad is generally performed to finish a main surface of the glass substrate in smooth mirror surface. Polishing of the glass substrate is performed as follows. A polishing pad comprising a polyurethane resin or the like is placed on a platen surface of a double side polishing apparatus or a single side polishing apparatus, a polishing surface of the polishing pad is subjected to a dressing treatment using a dressing jig to obtain given flatness and surface roughness, and the glass substrate and the polishing pad are then relatively moved in a state that a polishing surface of the polishing pad is pressed against the main surface of the glass substrate while supplying a polishing slurry containing abrasives between the glass substrate and the polishing pad, whereby the main surface of the glass substrate are polished.

One example of the present dressing jig is shown in FIG. 1. FIG. 1A is a schematically perspective view, and FIG. 1B is a cross-sectional view. In FIG. 1, 1 is the present dressing jig, and 2 is a plate surface (dressing surface) that dresses a polishing surface of a polishing pad.

Shape of the present dressing jig is not particularly limited so long as the shape thereof is a plate shape. Examples of the specific shape include a circle, a triangle, a quadrangle such as a square or a rectangle, and a polygon such as a pentagon or more. Structure of the present dressing jig is roughly classified into a dressing jig comprising a base and a dressing surface comprising other material formed on the surface of the base (type 1), and a dressing jig in which a base is not used, a plate itself is used as a dressing jig, and the plate surface is directly used as a dressing surface (type 2).

As the dressing jig of type 1, a dressing jig comprising a base comprising stainless steel or ceramics, and a dressing surface comprising at least one kind selected from the group consisting of a glass, ceramics, silicon, a stainless steel, aluminum, an aluminum alloy, titanium and a titanium alloy, fixed to the base may be mentioned. Abrasives (for example, diamond or ceramics) may be fixed to the base with a bonding material (metal, resin and the like).

Abrasives fixed to the surface of the dressing jig drop during a dressing treatment and adhere to the polishing pad surface, and the abrasives may cause generation of scratches on a glass substrate when polishing the glass substrate. For this reason, as the dressing jig of type 1, a dressing jig having a dressing surface formed thereon without using abrasives is preferably used.

Examples of the dressing jig of type 2 include a plate-like dressing jig comprising a glass, ceramics, silicon, aluminum, an aluminum alloy, titanium or a titanium alloy. The dressing jig of type 2 is simple and is low in production cost, and is therefore advantageous in cost when using a large amount of a dressing jig. Above all, a glass has excellent availability and low material unit price, and is therefore a preferable material.

When a glass is used as the dressing surface of the jig of type 1 and the dressing jig of type 2, kind of the glass used is not particularly limited. Amorphous glass, crystallized glass, reinforced glass comprising a glass and a reinforcing layer formed on the surface thereof, and the like can be used. Of these, amorphous glass is preferred in that an average surface roughness Ra of the dressing surface can easily be adjusted to given roughness. Color of the glass used is not particularly limited. Use of a glass colored in color different from that of a glass substrate product to be polished is preferred in that the glass used as a dressing jig can easily be distinguished from the glass substrate product and incorporation of a glass-made dressing jig into the glass substrate product can be prevented.

The present dressing jig is preferred to dress a polishing pad for polishing a main surface of the glass substrate, and a treatment surface of the dressing jig is adjusted to a specific surface roughness as described hereinafter. Therefore, the present jig does not require a dressing treatment again, and overcomes the problem such that the conventional technology is poor in productivity.

The present dressing jig is that arithmetic average roughness (hereinafter referred to “average surface roughness” for simplicity) Ra of a surface of a side grinding a polishing pad, that is, a side for performing a dressing treatment (hereinafter sometimes referred to as “dressing surface”) is from 0.10 μm to 2.5 μm. When the average surface roughness Ra is less than 0.1 μm, convex portions on the polishing surface of the polishing pad cannot appropriately be cut and removed, and roughness of the polishing surface of the polishing pad cannot quickly be decreased. Therefore, much time is required to adjust roughness of the polishing surface of the polishing pad. On the other hand, when the average surface roughness Ra exceeds 2.5 μm, the polishing surface of the polishing pad is excessively roughly ground, and fresh convex portions are continued to form. Therefore, a dressing treatment is required again to adjust a surface roughness of the polishing surface of the polishing pad, and additionally, durability of the polishing pad may greatly be decreased.

The average surface roughness Ra of the dressing surface of the present dressing jig is preferably 2.0 μm or less, further preferably from 0.3 to 2.0 μm, and most preferably from 0.3 to 1.7 μm.

In the present specification, the average surface roughness Ra of the dressing jig is a value measured with a stylus surface roughness measuring instrument according to JIS B 0601-2001. Surface roughness of a dressing jig is measured after calibration using a standard sample having a given surface roughness before the measurement.

The dressing surface of the present dressing jig is characterized by controlling surface properties to a specific surface roughness as described before. A method for controlling surface properties is not particularly limited, and examples of the method include adjustment methods such as a grinding method, an ion milling method, a blast method, a dry etching method and a wet etching method.

The average surface roughness Ra of the dressing surface is that the surface abrades away as the dressing treatment proceeds, and the numerical value of the average surface roughness Ra is decreased. By that the numerical value of the average surface roughness Ra of the treating surface becomes small during the dressing treatment, a stepwise dressing treatment as if using a plurality of dressing jigs having different average surface roughness Ra can be conducted with one dressing jig.

In the present dressing jig, the dressing surface abrades away during the dressing treatment, and the numerical value of the average surface roughness Ra of the dressing surface becomes small. In the present specification, amount of change of the average surface roughness Ra of the dressing surface is represented by {(average surface roughness Ra of dressing surface before dressing)-(average surface roughness Ra of dressing surface after dressing)}÷(average surface roughness Ra of dressing surface before dressing)×100 (%). The polishing surface of the polishing pad can efficiently be adjusted as the amount of change of the average surface roughness Ra is large.

In the present dressing jig, when the amount of change is 15% or more, a stepwise dressing treatment as if using a plurality of dressing jigs having different average surface roughness Ra can be conducted by one dressing jig, and this is preferred. The amount of change is preferably 25% or more, more preferably 35% or more, and particularly preferably 45% or more.

The present dressing jig abrades away during the dressing treatment, and the average surface roughness Ra becomes small. However, the dressing surface having small average surface roughness Ra can easily be regenerated using the method for controlling surface properties (such as a grinding method, an ion milling method, a blast method, a dry etching method and a wet etching method) described before. As a result, the present dressing jig can repeatedly be used as a dressing jig, which is economical.

A method for polishing a glass substrate using the present dressing jig is described below. Polishing of the glass substrate is generally performed by the following procedures.

(a) A polishing pad is mounted on a surface of a platen of a polishing apparatus, a polishing surface of the polishing pad is subjected to a dressing treatment using the present dressing jig, and the polishing surface of the polishing pad is adjusted to given flatness and surface roughness. Specifically, a carrier for a dressing treatment is placed on the polishing pad mounted on a lower platen, and a dressing jig is arranged in a hole for the carrier for dressing treatment. An upper platen having the polishing pad mounted thereon is descended to press the dressing surface with the polishing surfaces of the polishing pads from upper and lower directions, and the dressing jig and the polishing pad are relatively moved while supplying a dressing liquid between the polishing surface of the polishing pad and the dressing surface of the dressing jig from a dressing liquid supply hole of the upper platen, thereby performing a dressing treatment of the polishing pad. The dressing liquid used includes pure water after pH adjustment and various functional waters. The dressing liquid may contain abrasives, a water-soluble polymer or a surfactant. Pressure of a polishing platen when conducting the dressing treatment is preferably from 60 to 100 g/cm².

When the polishing pad is first used, closed pores on the surface are subjected to a pore-opening treatment before the dressing treatment. The pore-opening treatment is conducted using, for example, a pore-opening treatment exclusive apparatus, or a diamond dressing jig having an average surface roughness Ra of 2.5 μm or more after mounting the polishing pad on a platen surface of a polishing apparatus. After the pore-opening treatment, a dressing treatment is applied to the polishing pad using the present dressing jig to adjust the polishing surface of the polishing pad to given flatness and surface roughness, and polishing of a glass substrate product is conducted.

After the pore-opening treatment and dressing treatment of the polishing pad, the polishing pad surface may appropriately be cleaned using brush cleaning or high-pressure water cleaning.

A schematically cross-sectional view of the polishing pad after the dressing treatment is shown in FIG. 2. In FIG. 2, 10 is a polishing pad, and 101 is a polishing layer comprising a urethane resin having large pores 105 formed therein. 102 is a base layer comprising a urethane resin having small pores 106 formed therein. 103 is a substrate (comprising, for example, PET resin), and 104 is a polishing surface. FIG. 2A shows the polishing surface 104 of the polishing pad after the pore-opening treatment but before the dressing treatment with the present dressing jig, and FIG. 2B shows the polishing surface 104 the polishing pad after the dressing treatment with the present dressing jig. The pad polishing surface is adjusted smooth by the present dressing jig.

The average surface roughness Ra of the polishing pad surface after the dressing treatment using the present dressing jig is 2.4 μm or less. When polishing is conducted with a polishing pad having an average surface roughness of a polishing surface exceeding 2.4 μm, micro waviness characteristics and arithmetic average roughness characteristics of a glass substrate product may be deteriorated. The average surface roughness Ra of the polishing pad surface after the dressing treatment is 2.4 μm or less, preferably 2.2 μm or less, and further preferably 2.0 μm or less.

In the present specification, the average surface roughness Ra of the polishing pad surface is a value measured with a stylus surface roughness measuring instrument according to JIS B 0601-2001. Surface roughness of a polishing pad surface is measured after calibration using a standard sample having a given surface roughness before the measurement.

(b) A glass substrate product is polished using a polishing pad after a dressing treatment. Specifically, a carrier for polishing is placed on the polishing pad mounted on a lower platen, and a glass substrate is set in a hole of the carrier for polishing. An upper platen having the polishing pad mounted thereon is descended to press the glass substrate with the polishing surfaces of the polishing pads from upper and lower directions. The glass substrate and the polishing pad are relatively moved while supplying a polishing slurry between the polishing surface of the polishing pad and a main surface of the glass substrate from a polishing slurry supply hole of the upper platen, thereby polishing the glass substrate.

When the polishing of the glass substrate is continuously conducted, abrasives and glass debris are adhered to the polishing surface of the polishing pad, resulting in occurrence of clogging of the polishing pad. The clogging inhibits flow of the polishing slurry supplied between the polishing surface of the polishing pad and the glass substrate, resulting in decrease in a polishing rate. Additionally, abrasives and glass debris adhered to the polishing surface of the polishing pad are pressed to a main surface of the glass substrate during polishing, resulting in scratching the glass substrate and increasing adhered contaminations that are difficult to remove by cleaning. For this reason, it is necessary to grind the polishing surface of the polishing pad periodically to regenerate the polishing pad. The present dressing jig can be used to eliminate clogging of the polishing pad, which is periodically carried out in the course of the continuous polishing.

In the case where water-soluble polymers and surfactants, used when manufacturing a polishing pad remain, those materials flocculate abrasives during polishing, resulting in clogging of the polishing pad and decrease in life of a polishing slurry (circulating use). When the polishing pad is subjected to a dressing treatment using the present dressing jig, water-soluble polymers and surfactants, remaining in the polishing pad can effectively be removed as a subsidiary effect, and this is preferred.

The glass substrate to be polished in the present invention is not particularly limited. Specific examples of the glass substrate include glass substrates for magnetic recording medium, photomask, display of liquid crystal or organic EL, and the like. Kind of a glass of the glass substrate is appropriately selected from glasses suitable for the respective uses. The glass may be amorphous glass, crystallized glass, and reinforced glass having a reinforcing layer on a surface layer of a glass substrate (for example, chemically strengthened glass). A method for manufacturing a glass substrate before processing (hereinafter referred to as a “raw glass substrate”) is not particularly limited. The glass substrate may be manufactured by a float process and may be manufactured by a press molding process.

Of the above glass substrates, a glass substrate for magnetic recording medium is required to have severe level of surface characteristics as compared with those required in other glass substrate products. The present dressing jig and the polishing method using the present dressing jig are most preferably applied to such a glass substrate for magnetic recording medium.

Surface characteristics of the glass substrate for magnetic recording medium are described below. Indexes indicating the surface characteristics include the arithmetic average roughness μWa of micro waviness having a period of from 150 μm to 1,200 μm, and micro waviness Wq having a period of from 40 μm to 200 μm.

The μWa of the glass substrate for magnetic recording medium is that the average value of the values measured at six sites in total of 0°, 120° and 240° in the intermediate portion of the recording and reproducing regions of the top and bottom main surfaces is preferably 0.12 nm or less, more preferably 0.11 nm or less, and further preferably 0.10 nm or less. Difference (scattering of values measured at the above six sites) of micro waviness μWa measured in the same glass substrate for magnetic recording medium is preferably 0.020 nm or less, more preferably 0.019 nm or less, and further preferably 0.017 nm or less.

In the present specification, the μWa is arithmetic average roughness of micro waviness having a period of from 150 μm to 1,200 μm measured using a scanning white light interferometer, and the measurement region was 1.0 mm×0.7 mm.

One example of μWa measurement sites and measurement regions of a glass substrate 20 for magnetic recording medium, having a diameter of 65 mm is shown in FIG. 3. In FIG. 3, 201 is a main surface, 202 is a center of a disk, and 203 is the μWa measurement regions. “a” is 0.7 mm, “b” is 1.0 mm, and “c” is 15.75 mm. p1 to p3 indicate the μWa measurement sites, and are located at a position of 15.75 mm from the center of the disk at an interval of 120°. In the following description of the drawings, the same reference numerals and signs indicate the same elements.

The Wq of the glass substrate for magnetic recording medium is that the average value when measured at regions of six sites in total of an inner diameter side region, an intermediate region and an outer diameter side region in the recording and reproducing region of top and bottom main surface is preferably 2.0 nm or less, more preferably 1.7 nm or less, and further preferably 1.5 nm or less. Similarly, the difference (scattering of values measured at the above six sites) of micro waviness Wq measured in the same glass substrate for magnetic recording medium is preferably 1.0 nm or less.

In the present specification, the micro waviness Wq is measured using a light scattering surface viewer. The micro waviness Wq is micro waviness having a period of from 40 μm to 200 μm. Laser light having a wavelength of 405 nm enters a surface of an object to be measured at an angle of 60°, and reflection light from the object to be measured is detected, thereby obtaining information of height of a main surface. The measurement region was a region gone around in a circumferential direction with a width of 1.0 mm. The measuring position in a circumferential direction (position from a center of the glass substrate for magnetic recording medium) can optionally be selected.

One example of Wq measurement sites and measurement regions of the glass substrate 20 for a magnetic recording medium having a diameter of 65 mm is shown in FIG. 4. In FIG. 4, 204 to 206 indicate Wq measurement sites, wherein 204 is an inner diameter side region, 205 is an intermediate region and 206 is an outer diameter side region. “d” is a position of 12.8 mm from a center 202 of a disk, “e” is a position of 21.0 mm from the center 202 of a disk, and “f” is a position of 30.5 mm from the center 202 of a disk.

In the recording and reproducing region of the glass substrate for a magnetic recording medium, the value of the average surface roughness Ra and the in-plane scatter are preferably small. The average value of the average surface roughness Ra measured at two positions in total of 0° and 180° in the intermediate portion of the recording and reproducing region is preferably 0.15 nm or less, more preferably 0.13 nm or less, and further preferably 0.10 nm or less.

In the present specification, the average surface roughness Ra of the glass substrate for a magnetic recording medium is measured using an atomic force microscope. The measurement region is 1.0 μm×0.5 μm.

One example of measurement sites and measurement regions of the average surface roughness Ra of the glass substrate 20 for a magnetic recording medium having a diameter of 65 mm is shown in FIG. 5. In FIG. 5, 207 indicates the measurement sites of the average surface roughness Ra, “g” is 0.5 μm, “h” is 1.0 μm and “i” is 15.75 mm. q1 and q2 indicate positional relationship of measurement sites of the average surface roughness Ra, are position of 15.75 mm from the center of a disk, and are located at an interval of 180°.

The surface characteristics of the glass substrate for a magnetic recording medium are that the average value of μWa measured in the recording and reproducing region of the glass substrate for a magnetic recording medium is preferably 0.10 nm or less, and the average value of Wq is more preferably 1.5 nm or less. In addition to the surface characteristics of the glass substrate for a magnetic recording medium, the average value of the average surface roughness Ra is most preferably 0.10 nm or less.

Production steps of a glass substrate for magnetic recording medium and a magnetic disk generally include the following steps. (1) A raw glass substrate formed by a float process or a press-molding process is processed into a disk shape, and chamfering processing is then applied to an inner peripheral side surface and an outer peripheral side surface. (2) Wrapping processing is applied to upper and lower main surfaces of a glass substrate. (3) Edge polishing is applied to a side portion and a chamfering portion of a glass substrate. (4) Polishing is applied to the upper and lower main surfaces of a glass substrate. The polishing step is that only primary polishing may be conducted, primary polishing and secondary polishing may conducted, and tertiary polishing may be conducted after secondary polishing. The polishing method using the present dressing jig can be applied to any step of from the primary polishing to the tertiary polishing. In particular, the polishing method is preferably applied to the secondary method or the tertiary method. (5) Precision cleaning of the glass substrate is conducted, thereby manufacturing a glass substrate for magnetic recording medium. (6) A thin film such as a magnetic layer is formed on the glass substrate for a magnetic recording medium, thereby manufacturing a magnetic disk.

In the above-described production steps of a glass substrate for a magnetic recording medium and a magnetic disk, glass substrate cleaning (in-process cleaning) and etching of a surface of a glass substrate (in-process etching) may appropriately be carried out between the respective steps. Furthermore, when high mechanical strength is required in a glass substrate for a magnetic recording medium, a strengthening step (for example, chemically strengthening step) of forming a reinforcing layer on a surface layer of a glass substrate may be carried out before the polishing step, after the polishing step, or during the polishing step.

EXAMPLES

The present invention is further described below based on the above-described example that the present dressing jig and a polishing method using the present dressing jig are applied to tertiary polishing during the production steps of a glass substrate a for magnetic recording medium and a magnetic disk, but the invention is not construed as being limited thereto.

Preparation of Glass Substrate for Magnetic Recording Medium:

A glass substrate comprising SiO₂ as a main component, formed by a float process was processed into a donut-like circular glass substrate (disk-like glass plate having circular hole at the center) to prepare a glass substrate for a magnetic recording medium having an outer diameter of 65 mm, an inner diameter of 20 mm and a plate thickness of 0.635 mm.

An inner peripheral side surface and an outer peripheral side surface of the donut-like circular glass substrate were subjected to chamfering processing so as to obtain a glass substrate for a magnetic recording medium having a chamfering width of 0.15 mm and a chamfering angle of 45°, the upper and lower main surfaces were lapped using aluminum abrasives, and the abrasives were removed by cleaning.

The inner peripheral side surface and the inner peripheral chamfered portion were polished using polishing brush and cerium oxide abrasives to remove scratches of the inner peripheral side surface and the inner peripheral chamfered portion, and the inner peripheral edge was subjected to polishing processing so as to form a mirror surface. The glass substrate after inner peripheral edge polishing was subjected to scrub cleaning using an alkaline detergent, and ultrasonic cleaning in a state of dipping in an alkaline detergent solution, thereby removing abrasives by cleaning.

The outer peripheral side surface and the outer peripheral chamfered portion of the glass substrate after inner peripheral edge polishing were polished using polishing brush and cerium oxide abrasives to remove scratches of the outer peripheral side surface and the outer peripheral chamfered portion, and the outer peripheral edge was subjected to polishing processing so as to form a mirror surface. The glass substrate after the outer peripheral edge polishing was subjected to scrub cleaning using an alkaline detergent, and ultrasonic cleaning in a state of dipping in an alkaline detergent solution, thereby removing abrasives by cleaning.

Primary to Tertiary Polishings of Glass Substrate for Magnetic Recording Medium:

The glass substrate after the edge polishing was subjected to primary polishing of the upper and lower main surfaces by a double side polishing apparatus (manufactured by SpeedFam Co., Ltd., trade name: DSM-9B-5PV-4 MH) using a hard urethane-made polishing pad and a polishing slurry containing cerium oxide abrasives (polishing slurry composition comprising cerium oxide having an average particle diameter (hereinafter referred to an “average particle size”) of about 1.1 μm as a main component) as polishing jigs, and cerium oxide was then removed by cleaning.

The glass substrate after the primary polishing was subjected to polishing of the upper and lower main surfaces by a double side polishing apparatus using a soft urethane-made polishing pad and a polishing slurry containing cerium oxide abrasives having an average particle size smaller than that of the above cerium oxide abrasives (polishing slurry composition comprising cerium oxide having an average particle size of about 0.5 μm as a main component) as polishing jigs, and cerium oxide was then removed by cleaning.

The glass substrate after the primary polishing and the secondary polishing is subjected to finish polishing (tertiary polishing). The upper and lower main surfaces were subjected to polishing processing by a double side polishing apparatus using a soft urethane-made polishing pad and a polishing slurry containing colloidal silica (polishing slurry composition comprising colloidal silica having an average particle size of primary particles of from 20 to 30 nm as a main component) as polishing jigs of the finish polishing (tertiary polishing), and were polished to a removal of 2 μm in total in the thickness direction of the upper and lower main surfaces. The polishing was conducted under main polishing processing pressure of 80 g/cm² at a number of rotations of a platen of 40 rpm.

A soft polishing pad having the constitution shown in FIG. 2 was used as a polishing pad for the tertiary polishing.

Pore-unopened soft polishing pad was used in the present example. Therefore, a pore opening treatment was first conducted. A polishing pad is mounted on a polishing platen, and a pore opening treatment was conducted with a #400 diamond dressing jig. Diameter of open pore (diameter in long axis direction) in a polishing surface was confirmed with a microscope. The diameter of open pore (diameter in long axis direction) was observed at six sites in total of an inner peripheral portion, a central portion and an outer peripheral portion of polishing pads mounted on the upper and lower platens of a double side polishing apparatus, and the pore opening treatment was conducted until the open pore diameter (diameter in long axis direction) is 10 μm or more at all of the measurement sites. Average surface roughness Ra of the #400 diamond dressing jig is shown in Example 4 in Table 1.

The polishing pad after the pore opening treatment was cleaned by brush cleaning to remove polishing pad debris and diamond abrasion debris adhered to a polishing surface, and a dressing treatment was then applied to the polishing pad.

Example 1 Working Example

Dressing treatment of a polishing pad was conducted using a disk-like glass substrate (diameter: 65 mm) having an average surface roughness Ra of 1.25 μm, comprising SiO₂ as a main component as a dressing jig, thereby conducting finish polishing of a glass substrate for a magnetic recording medium. The dressing treatment was carried out while supplying a dressing liquid containing colloidal silica (colloidal silica having an average grain size of primary particles of from about 20 to 30 nm). The average surface roughness Ra of the dressing jig after the dressing treatment was 0.35 and an amount of change of the average surface roughness Ra before and after the dressing treatment was 72%. The average surface roughness Ra of the polishing surface of the polishing pad after the dressing treatment was 1.85 μm.

Example 2 Comparative Example

The dressing treatment was conducted in the same manner as in Example 1, except for using a disk-like glass substrate having an average surface roughness Ra of 0.08 μm as the dressing jig, thereby conducting finish polishing of a glass substrate for a magnetic recording medium. The average surface roughness Ra of the dressing jig after the dressing treatment was 0.07 μm, and an amount of change of the average surface roughness Ra before and after the dressing treatment was 13%. The average surface roughness Ra of the polishing surface of the polishing pad after the dressing treatment was 2.45 μm.

Example 3 Comparative Example

The dressing treatment was conducted in the same manner as in Example 1, except for using a dressing jig having an average surface roughness Ra of 2.75 (#600 diamond dressing jig) as the dressing jig, thereby conducting finish polishing of a glass substrate for a magnetic recording medium.

The average surface roughness Ra of the polishing surface of the polishing pad after the dressing treatment of Example 1 could be adjusted low as compared with Example 2 which is Comparative Example. It is presumed from this fact that the present dressing jig can conduct a stepwise dressing treatment by one dressing jig as if the dressing treatment was conducted using a plurality of dressing jigs having different average surface roughness Ra by that the average surface roughness Ra greatly changes during the dressing treatment.

The average surface roughness Ra of the dressing jig and the average surface roughness Ra of the polishing surface of the polishing pad after the dressing treatment were measured using a stylus surface roughness measuring instrument (manufactured by Tokyo Seimitsu Co., Ltd., product name: Handy Surf E-30A, stylus type: SM-10A).

The average surface roughness Ra of the dressing jigs of Example 1 and Example 2 was measured by scanning a stylus 5 mm toward the outer peripheral portion (diameter direction) from the central portion in a region 22.5 mm outside from the central portion of the jig. The measurement was conducted three times in the measurement region, and its average value was obtained.

The average surface roughness Ra of the dressing jig of Example 3 was measured by scanning a stylus 5 mm toward the outer peripheral portion (diameter direction) from the central portion in a region 44 mm outside from the central portion of the jig. The measurement was conducted three times in the measurement region, and its average value was obtained. The average surface roughness Ra of the #400 diamond dressing jig used in the pore opening treatment of the polishing pad was measured in the same manner.

The average surface roughness Ra of the polishing surface of the polishing pad after the dressing treatment was measured on the polishing surface of the polishing pad mounted on the lower platen. The average surface roughness Ra was measured by scanning a stylus 5 mm toward a circumferential direction (direction of from the observer's left to the observer's right) in the region 290 mm outside from the central portion of the polish apparatus. The measurement was conducted five times in the measurement region, and its average value was obtained.

The glass substrate after the tertiary polishing using the polishing pad having been subjected to the above dressing treatment was dipped in a solution adjusted to the same pH as that of the polishing slurry for finish polishing. Scrub cleaning by an alkaline detergent, ultrasonic cleaning in a state of being dipped in an alkaline detergent solution and ultrasonic cleaning in a state of being dipped in pure water were sequentially conducted, followed by drying with IPA steam.

After cleaning and drying, surface characteristics of the glass substrate for magnetic recording medium were measured. Evaluation of the surface characteristics was conducted by measuring a glass substrate of first lot, polished just after the dressing treatment.

The μWa was measured using a scanning white light interferometer (manufactured by Zygo, product name: Zygo New View 5032). The measurement was conducted at the positions of six sites in total of 0°, 120° and 240° in the intermediate portion 203 (position 15.75 mm outside from the 202 of a disk) of the recording and reproducing region of the upper and lower main surfaces of the glass substrate 20 for magnetic recoding medium, as shown in FIG. 3. Six glass substrates were extracted per one lot (25 plates), and measured. Average value of μWa and scattering values in the same glass substrate surface and the same lot were obtained from the measurement results of 36 sites in total.

Measurement results of μWa of the Working Example and Comparative Examples are shown in Table 1. The average value and the scattering value of μWa of the glass substrate for magnetic recording medium polished by the polishing surface of the polishing pad having been subjected to the dressing treatment using the dressing jig of the present invention are small as compared with those of Comparative Examples, and good results were obtained.

The Wq was measured using a light scattering surface viewer (manufactured by Candela, product name: OSA6100). The measurement was conducted in six regions in total of the inner diameter side region 204 (position of from 12.8 mm to 13.8 mm from the center 202 of a disk), the intermediate region 205 (position of from 21.0 mm to 22.0 mm from the center 202 of a disk) and the outer diameter side region 206 (position of from 30.5 mm to 31.5 mm from the center 202 of a disk) in the recording and reproducing regions of the upper and lower main surfaces 201 of the glass substrate 20 for magnetic recording medium, as shown in FIG. 4. Three glass substrates were extracted per one lot (25 plates), and measured. Average value of micro waviness Wq and scattering value in the same glass substrate surface and the same lot were obtained from the eighteen measurement results in total.

The measurement results of Wq are shown in Table 1. The average value and the scattering value of the micro waviness Wq of the glass substrate for magnetic recording medium polished by the polishing surface of the polishing pad having been subjected to the dressing treatment using the present dressing jig are small as compared with those of Comparative Examples, and good results were obtained.

The average surface roughness Ra of the glass substrate for a magnetic recording medium was measured using an atomic force microscope (manufactured by Digital Instruments, product name: Nano Scope D3000). The measurement was conducted at positions of two sites of 0° and 180° at an intermediate portion 207 (position of 15.75 mm from the center 202 of a disk) of the recording and reproducing region of the main surface 201 of the glass substrate 20 for magnetic recording medium, as shown in FIG. 5. Two glass substrates were extracted per one lot (25 plates), and measured. The average value of the average surface roughness Ra was obtained from the measurement results at four sites in total. The measurement results are shown in Table 1.

The average value of the average surface roughness Ra of the glass substrate for a magnetic recording medium polished by the polishing surface of the polishing pad having been subjected to the dressing treatment using the present dressing jig is small as compared with those of Examples 2 and 3 that are Comparative Examples, and good results were obtained.

In the case that a surfactant and the like that coagulate abrasives in a polishing slurry remained in the polishing pad, use of the dressing jig of Example 1 can quickly remove the surfactant and the like remained in the polishing pad as compared with Example 2 that is Comparative Example.

The dressing treatment was conducted while supplying a polishing slurry, the polishing slurry after the dressing treatment was recovered at the time of each dressing treatment, particle size distribution of abrasives in the polishing slurry recovered was measured with a dynamic light scattering particle size distribution measuring instrument (Otsuka Electronics Co., Ltd., product name: FPAR-1000), and the residual amount of a surfactant remained in the polishing pad was evaluated. The results obtained are shown in FIG. 6. The degree of coagulation of FIG. 6 is a value obtained by dividing D50 value (particle diameter when cumulative frequency % of scattering strength histogram is 50%) of particle size distribution measurement result of a polishing slurry recovered at the time of each dressing treatment by D50 value of unused polishing slurry. Abrasives in the polishing slurry recovered after the dressing treatment coagulate and D50 value is increased (the value of a degree of coagulation is increased) as the amount of a surfactant remained in the polishing pad is increased. Use of the dressing jig of Example 1 quickly decreases the value of a degree of coagulation as compared with use of the dressing jig of Example 2.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Dressing jig Before dressing treatment, 1.25 0.08 2.75 4.22 Average surface roughness Ra average value (μm) After dressing treatment, 0.35 0.07 2.65 average value (μm) After and before dressing treatment, 72 13 4 amount of change (%) Polishing pad surface After dressing treatment, 1.85 2.45 Average surface roughness Ra average value (μm) Main surface of glass substrate Average value (nm) 0.108 0.119 0.129 for a magnetic recording medium Maximum value (nm) 0.117 0.134 0.159 Micro waviness μWa Minimum value (nm) 0.100 0.107 0.110 Scattering (nm) 0.017 0.027 0.049 Main surface of glass substrate Inner diameter side region, 1.00 2.97 2.58 for a magnetic recording medium average value (nm) Micro waviness Wq Intermediate region, 1.27 2.42 1.63 averagevalue (nm) Outer diameter side region, 1.75 4.08 4.30 average value (nm) Average value (nm) 1.39 3.16 2.83 Scattering of average value in each 0.75 1.66 2.67 measurement region (nm) Main surface of glass Average value (nm) 0.148 0.201 0.169 substrate for a magnetic recording medium Arithmetic average roughness Ra

While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Incidentally, the present application is based on Japanese Patent Applications No. 2009-261999 filed on Nov. 17, 2009, and the contents are incorporated herein by reference.

Also, all the references cited herein are incorporated as a whole.

According to the present invention, a method for polishing a glass substrate, having excellent productivity by using a polishing pad having been subjected to a dressing treatment with the present dressing jig, and a method for producing a glass substrate can be provided. 

1. A dressing jig for a glass substrate polishing pad, having a plate shape and dressing a polishing pad for a glass substrate with a plate surface thereof, wherein the plate surface has a surface roughness of from 0.10 μm to 2.5 μm in terms of arithmetic average roughness Ra.
 2. The dressing jig for a glass substrate polishing pad according to claim 1, wherein a material of the plate surface of the dressing jig is at least one kind selected from the group consisting of a glass, ceramics, silicon, a stainless steel, aluminum, an aluminum alloy, titanium and a titanium alloy.
 3. A method for polishing a glass substrate, said method comprising dressing a polishing pad for a glass substrate using the dressing jig according to claim 1, and polishing a glass substrate with the polishing pad for a glass substrate.
 4. The method for polishing a glass substrate according to claim 3, wherein a polishing surface of the polishing pad after the dressing treatment has a surface roughness of 2.4 μm or less in terms of arithmetic average roughness Ra.
 5. The method for polishing a glass substrate according to claim 3, wherein an amount of change of the arithmetic surface roughness Ra of the dressing jig before and after the dressing treatment is 15% or more.
 6. A method for manufacturing a glass substrate, said method comprising the method for polishing a glass substrate according to claim
 3. 7. A method for manufacturing a glass substrate according to claim 6, wherein the glass substrate is a disk-like glass substrate for a magnetic recording medium and has a circular hole in a central portion thereof.
 8. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 7, wherein an average value of micro waviness μWa having a period of from 150 μm to 1,200 um measured using a scanning white light interferometer is 0.12 nm or less at positions of 0°, 120° and 240° in an intermediate portion of recording and reproducing regions of both main surfaces of the glass substrate for a magnetic recording medium, and difference of micro waviness μWa measured at said six sites is 0.020 nm or less.
 9. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 7, wherein an average value of micro waviness Wq having a period of from 40 μm to 200 μm measured using laser light having a wavelength of 405 nm at six sites of an inner diameter region, an intermediate region and an outer diameter region in recording and reproducing regions of both main surfaces of the glass substrate for a magnetic recording medium is 2.0 nm or less.
 10. The method for manufacturing a glass substrate for a magnetic recording medium according to claim 7, wherein an average value of arithmetic average roughness Ra measured using an atomic force microscope at two sites of 0° and 180° in an intermediate portion in a recording and reproducing region of the glass substrate for a magnetic recording medium is 0.15 nm or less. 